Areal rainfall estimation using moving cars as rain gauges – a modelling studyU. Haberlandt1 and M. Sester21Institute of Water Resources Management, Hydrology and Agricultural Hydraulic Engineering, Leibniz University of Hannover, Hannover, Germany2Institute of Cartography and Geoinformatics, Leibniz University of Hannover, Germany

Abstract. Optimal spatial assessment of short-time step precipitation for hydrological
modelling is still an important research question considering the poor
observation networks for high time resolution data. The main objective of
this paper is to present a new approach for rainfall observation. The idea
is to consider motorcars as moving rain gauges with windscreen wipers as
sensors to detect precipitation. This idea is easily technically feasible if
the cars are provided with GPS and a small memory chip for recording the
coordinates, car speed and wiper frequency. This study explores
theoretically the benefits of such an approach. For that a valid
relationship between wiper speed and rainfall rate considering uncertainty
was assumed here. A simple traffic model is applied to generate motorcars on
roads in a river basin. Radar data are used as reference rainfall fields.
Rainfall from these fields is sampled with a conventional rain gauge network
and with several dynamic networks consisting of moving motorcars, using
different assumptions such as accuracy levels for measurements and sensor
equipment rates for the car networks. Those observed point rainfall data
from the different networks are then used to calculate areal rainfall for
different scales. Ordinary kriging and indicator kriging are applied for
interpolation of the point data with the latter considering uncertain
rainfall observation by cars e.g. according to a discrete number of
windscreen wiper operation classes. The results are compared with the values
from the radar observations. The study is carried out for the 3300 km2
Bode river basin located in the Harz Mountains in Northern Germany. The
results show, that the idea is theoretically feasible and motivate practical
experiments. Only a small portion of the cars needed to be equipped with
sensors for sufficient areal rainfall estimation. Regarding the required
sensitivity of the potential rain sensors in cars it could be shown, that
often a few classes for rainfall observation are enough for satisfactory
areal rainfall estimation. The findings of the study suggest also a
revisiting of the rain gauge network optimisation problem.